This circuit describes AC voltage stabilizer ,/ automatic voltage regulator function with its input voltage range from AC 120 to 260V, at output voltage of AC 220 ( 1 ± 10%) V, Output power for this can be 300-1000W depending upon the transformer used.
AC voltage regulator circuit forms the power circuit with transformer and the voltage detection control circuit , as shown in Figure above . Voltage sensing circuit consists of four operational amplifiers formed out of an integrated circuit IC (Nl-N4),operating in comparator mode. Resistor, R7, capacitors C4, a potentiometer P, relay Kl-K4, are other sections of the circuit. . R7, RP, VD5, VD6 with C4 are for input voltage sensing circuit. Power supply for the circuit consists of series capacitor Cl, C2, resistor Rl, a bridge rectifier diode VDl-VD4, a filter capacitor C3,a zennor regulator diode and a transistor as VS . The transformer tapings connected to relay contacts from Nl to N4 get feed from voltage comparators .While input is at its lowest say 120 volt, relay K1, operates so that the input is boosted to the full by the autotransformer action of the transformer. As the input goes still higher the K1 is released and K2 is operated to connect the input to the next tap of the transformer to maintain the output. And so on for relay K3 at 220 volt input the output is 220 volt. As the input voltage goes higher than 240 say the relay contacts of K4 change the tapping of the transformer to 220 to maintain the output voltage at certain regulated percentage of 200+ – 10%.